The present invention relates to a method of sealing cooling holes provided on an aerofoil component.
Hollow aerofoil components such as turbine blades and nozzle guide vanes provided in gas turbine engines often comprise cooling holes, which extend from the hollow interior of the component to the exterior to provide a cooling air film in use, and thereby cool the surface of the component.
It is sometimes necessary to test the performance of such cooling holes, for example to validate a new component design, or to diagnose blockages during engine overhaul or repair.
Such aerofoil components often include a plurality of cooling holes arranged in closely spaced rows along the blade, as shown in FIG. 1. In order to test one cooling hole or a row of cooling holes, it is necessary to selectively seal the remaining cooling holes. Such seals must later be removed, so that other cooling holes can be tested, or to allow the blade to be reinstalled in an engine.
One previous method of selectively sealing cooling holes comprises using thin strips of tape to cover selected cooling holes. However, the tape can sometimes not provide a sufficiently robust seal, and is difficult to apply accurately. Additionally, tape is generally reinforced with quick setting epoxy such as Araldite™. The use of this material generally means that the components are unusable after the application of these materials.
A further known method comprises applying a ultra-violet (UV) curable material to one or more cooling holes, and subsequently curing the material using UV light. However, once cured, UV curable materials cannot be reformed. As a result, if the seal is found to be inadequate subsequent to curing, it cannot be repaired, and must instead be removed and reapplied. The UV curing process typically takes 30-60 seconds. UV curable material is also relatively expensive, and relatively large quantities are required to adequately seal cooling holes. UV curable material is also toxic, and is known to release toxic fumes during the curing process. The fumes need to be removed using local ventilation and the operator who applies the UV curable material will have to wear protective gloves and goggles.
The present invention provides an improved method of sealing cooling holes that addresses some or all of the aforementioned problems.